CAN network

U0073 — Control Module Communication Bus Off

Severity: high Drive with care, to a shop

What U0073 means

U0073 means a control module has detected a Bus Off condition on the CAN network, so modules can no longer exchange data. Normally all modules talk over a twisted pair of wires (CAN High and CAN Low) terminated with resistors at both ends. A wiring open or short, or a faulty module dragging the bus down, breaks this communication.

Symptoms

  • Several warning lights on at once
  • No-start condition
  • Dead or erratic gauges
  • Many U-codes stored in different modules
  • Features of the affected module unavailable
  • Scan tool cannot reach some modules

Possible causes

  1. Damaged CAN wiring (open, short, chafed harness)
  2. Faulty module pulling the bus down
  3. Corrosion in the diagnostic connector or junction connectors
  4. Aftermarket device plugged into the OBD port (alarm, tracker, dongle)
  5. Power supply or ground fault at a module
  6. Bus termination problem (failed resistor or broken line)

How to diagnose

  1. Run a full-module scan and map which modules respond and which do not
  2. Unplug any aftermarket device from the OBD port and rescan
  3. Inspect the diagnostic connector and main junction connectors for moisture and corrosion
  4. Measure resistance between CAN High and CAN Low at the connector (about 60 ohms on a healthy bus)
  5. Check CAN line voltages to ground against the manufacturer's specs
  6. Verify power, ground and fuses for the silent modules
  7. Inspect the harness for chafing and past repair or collision damage
  8. Following a documented procedure, unplug suspect modules one at a time and watch the bus

Common fixes

  • Repair the open or short and restore the damaged harness
  • Clean or replace corroded connectors and terminals
  • Remove the faulty aftermarket device from the OBD port
  • Restore the module's power or ground supply
  • Replace the faulty module loading the bus, with programming if required

Questions and answers

What does U0073 mean?

It means the CAN bus has shut down after errors and modules have stopped exchanging data. The cause is usually wiring, connectors or a faulty module.

Can I drive with U0073?

Only if the car runs normally and the brakes and steering feel right. Communication can drop at any time and disable key systems, so don't put off diagnosis.

Can an alarm or tracker cause U0073?

Yes, a faulty or poor-quality device in the OBD port can disturb the bus. Unplug it and see whether the code returns.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.